The combined rotary and orbital motion of the "Wankel"engine is now well known and there have also been numerous attempts to improve on the basic concept embodied in that engine. Many of these attempts have been directed at the chief problem in the Wankel, i.e., excessive wear and poor sealing at the point of contact between the rotor or piston and the wall of the combustion chamber. Possibly the ideal solution to this problem is to prevent rotational motion of the piston and allow only orbital motion. This has been attempted in a number of different constructions as shown typically in U.S. Pat. No. 3,703,344 to Reitter; 3,787,150 to Sarich; and 3,812,828 to Griffith. Most of the structures which limit the piston to orbital motion have a piston journalled on an eccentric shaft and a number of vanes between the piston and the cylinder housing. These vanes define distinct combustion chambers between themselves and reciprocate in the housing as the piston orbits. In some constructions the vanes themselves prevent rotation of the piston; however, sizeable bending and shear forces result on the vanes in these designs requiring heavy construction and producing high friction.
In a different version of a purely orbital motor, patented by Sarich and cited above, the tendency of the piston to rotate is prevented by means of two or more shafts, each having an eccentric portion on which the piston is mounted. This is mechanically equivalent to a parallelagram linkage between the piston and the cylinder to constrain the motion of the piston and take the pressure off the vanes. In the present invention, purely orbital motion of the piston is achieved through gearing associated with the cylinder, the piston, and the shaft to achieve a more efficient and rugged engine than in the prior art.